Summary
Buckling and its effects are topics of economic and technical interest as
ERD and horizontal wells become critical to maximizing recoverable reserves,
particularly in the continental United States and Alaska. Previous work has
resulted in important discoveries about drillstring buckling, but to date,
little testing has been performed on actual drillpipe in a controlled manner,
particularly in measuring drillstring whirl. As a result, there can be
disparities between theoretical predictions of buckling effects vs. actual
field results. These disparities can result in unrealistically high friction
factors required to bring calculated values close to actual data, or in many
cases, operational difficulties can result such as high torque, low rate of
penetration (ROP), drillstring failures, inability to maintain directional
control, or inability to reach the planned depth.
To learn more about drillstring behavior in buckling conditions, a
full-scale buckling test fixture was developed to evaluate the effects of
buckling on 2 7/8-, 3 1/2-, and 4-in. drillpipe while sliding and rotating
inside 7-in. casing. The test fixture incorporated a variety of sensors and
cameras to characterize torque, drag, vibration, and drillstring deformation
under buckling loads. As part of the test program, low-friction nonrotating
protectors were also tested to measure performance under buckling
conditions.
The test results show that drillstring buckling occurs at far lower loads
than predicted by current models, possibly caused by minor deformations
inherent in real drillpipe. The results also show that for a given amount of
torque or drag, protectors increased the available compressive load by 20 to
30% and substantially reduced vibration caused by drillstring whirl.
The test results were used to develop a new semiempirical buckling model
that predicts contact forces resulting from drill-drag modeling software in
which it was compared against actual data from a large number and variety of
wells. The results show an ability to more accurately predict torque, drag, and
vibration caused by buckling and whirl.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
25 May 2011
- Meeting paper published:
7 May 2011
- Revised manuscript received:
11 August 2011
- Manuscript approved:
31 August 2011
- Published online:
22 December 2011
- Version of record:
27 December 2011
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